Tuning indicator tube



web 19, 1930 R T, ORTH TUNINGINDICATOR TUBE Filed July 27, 1934 INVENTOR RICHARD T. ORTH Patented Mar. 19, 1935 UNITED STATES TUNING INDICATOR TUBE.

Richard Tempe] Orth, Maplewood, N, J assignor to Radio Corporation of America, a corporation of Delaware Application July 27, 1934, Serial No. 737,167

Claims.

My invention relates to electron discharge devices, more particularly to such devices used as visual indicators of voltage and having a fluorescent electrode which is rendered luminous and 5 produces the appearance of a column of light the length of which depends upon the magnitude of the applied voltage, a device of this character being particularly useful as a tuning indicator in radio receiving sets. The present invention is an improvement over a device of the general character described and claimed in a co-pending application of Browder J. Thompson, Serial No. 736,833, filed July 25, 1934 and assigned to the same assignee as the present invention.

One embodiment of such a device useful as a tuning indicator, and described in the Thompson application above referred to, comprises an envelope having a straight indirectly heated equipotential cathode, a variable pitch grid concentric with and surrounding the cathode and a mesh anode coated with fluorescent material concentric with and surrounding the cathode and grid. In operation electrons flow from the cathode to the plate with sufiicient velocity to bombard the plate and render it luminous. The control grid is so connected in a radio receiving circuit that when the circuit is tuned to resonance with an incoming signal the luminous portion of the plate is of predetermined length. Preferably the device is so connected that the luminous portion of the anode is of minimum length when the circuit is tuned to resonance.

It is an object of my invention to provide an improved electron discharge device of this general character which is particularly suitable for use as a tuning indicator in a radio receiving set in which resonance is indicated by a brilliant luminous glow on the anode.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a perspective view, with parts broken away, of an electron discharge device made in accordance with my invention; Figure 2 is a horizontal section taken along line 2-2 of Figure 1; and Figure 3 is a schematic diagram of a portion of a radio receiving circuit using an electron discharge device such as shown in Figure 1.

The electron discharge device or tuning indicator tube shown in Figure 1 comprises an evacuated envelope 10 provided with the usual stem and press 11 and base 12. Supported from the press are a cathode 13, preferably the conventional indirectly heated unipotential type, and a grid 14 concentric and preferably coextensive with and surrounding the cathode, the pitch between the turns varying preferably from one end of the grid to the other and shown in this particular embodiment with the greatest pitch at the bottom of the grid. In accordance with my invention, I position concentric and preferably coextensive with and surrounding the cathode and grid a solid sheet anode 15 provided with a 1ongitudinal opening 16 parallel to the cathode 13. Positioned in registry with this longitudinal opening and substantially coextensive with the cathode 13 is an auxiliary rod anode 17 having a coating fluorescent under electron bombardment and to which in normal operation is applied a positive voltage with respect to the grid and cathode. Electrons emitted from the cathode and striking the auxiliary anode with sufficient velocity cause it to fluoresce.

In the type of tuning indicator tube in which a fluorescent mesh anode is positioned concentric with and surrounding the cathode, most of the glow appears on the inside of the mesh anode, the cause for this, it is believed, being that most of the electrons emitted from the cathode strike the screen on the interior of the screen. The resultant luminosity therefore does not appear to be as brilliant as it would otherwise appear if the outer surface of the mesh were struck by electrons with sufficient velocity to cause it to fluoresce.- The increased brilliancy of the luminous glow in'a tube made in accordance with my invention is believed to result from the following action. The electrons travel radially outward from the cathode and some pass by the auxiliary rod anode 17 in the space between the rod anode and the sides of the longitudinal opening 16 in the cylindrical anode 15. Due to the fact that this auxiliary anode has a positive voltage applied to it, electrons traveling to the wall of the envelope or bulb are drawn back with sufiicient velocity to strike the surface of the rod anode facing the envelope wall to cause it to fiuoresce so that the rod is fluorescent over its entire surface, giving a brilliant glow visible from the exterior of the envelope. This luminosity can be increased by increasing the positive potential on the rod anode with respect to the cylindrical anode 15, since this causes not only a greater concentration of the electrons on the rod anode but also increases the velocity with which the electrons strike the rod anode.

With no negative or a small negative bias on the grid, electrons from along the whole length of the cathode 13 reach the rod anode causing it to fiuoresce over its entire coated surface. This gives the appearance of a long narrow column of bright light. Applying a negative bias to the grid 14 and gradually increasing the bias, decreases progressively and lengthwise of the cathode the electron flow from the cathode to the auxiliary rod anode, so that the luminous portion of the rod anode is correspondingly deuse of to indicate resonance in a radio receiving set.

-,Referring to Figure 3, where there is shown a portion of a radio receiving circuit embodying a tuning indicator tube made in accordance with my invention, the transformer 20 which may be a radio frequency or an intermediate frequency transformer and may be coupled to preceding stages, has its secondary tuned by means of variable condenser 21. The alternating voltage whichappears across the terminals of condenser 21 and the secondary of transformer 20 when tuned to an incoming signal is applied between plate 22 and cathode 23 of a diode detector or rectifier 24, the rectified current resulting in a voltage drop across resistor 25, the end connected to the condenser 21 acquiring a negative potential with respect to the end connected to the cathode 23 of tube 24. The resistor 25 is by-passed for radio frequency or intermediate frequency currents by means of lay-passing condenser 26. The voltage drop across the resistor 25 is applied to the tuning indicator tube 10 to indicate resonance.

The cathode 13 of the tuning indicator tube 10 is connected to the positive end of the resistor 25 while the grid 14 is connected to the negative end of resistor 25. The anode 15 and auxiliary rod anode 17 which may be connected together are connected to a positive potential with respect to the grid and cathode. It is possible to use the tube as a combined triode and tuning indicator tube if proper connections are made to the anode 15 and auxiliary rod anode 17.

With no signal voltage across the diode 24 and hence no current thru resistor 25 both ends of resistor 25 are at the same potential so that there is no bias on the grid 14 with respect to cathode 13 of the tuning indicator tube 10. This permits the rod anode 17 to fiuoresce along its whole length because electrons reach it from along the whole length of the cathode 13. As the circuit comprising the secondary of transformer 20 and variable condenser 21 is tuned to resonance with an incoming signal a voltage drop develops across the resistor 25, the left-hand end of the resistor 25 assuming a negative value with respect to the right hand end. As resonance is approached the rectified current thru the diode and resistor 25 increases and the left end of the resister 25, that is the end connected to the grid 14 of the tuning indicator tube 10, becomes increasingly negative so that increasingly negative bias is applied to control grid 14. As explained above this increase in negative bias results in a progressive decrease in the length of the luminous portion of the rod anode, the bias on the grid being of a maximum negative value and the length of the luminous portion of the rod anode being the shortest when the detector circuit is tuned to resonance with an incoming signal.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as ngw'is 1. An electron discharge device having an envelope, a straight cathode within said envelope for emitting electrons, a solid sheet electrode surrounding said cathode and having a longitudinal opening parallel to said cathode, a straight electrode coated with fluorescent material positioned in registry with said opening, and a variable pitch grid positioned between said cathode and said straight electrode for decreasing progressively and lengthwise of the cathode the electron flow from the cathode to said straight electrode when a progressively varying voltage is applied to the grid.

2. An electron discharge device having an envelope, a straight cathode within said envelope for emitting electrons, an electrode surrounding said cathode and having a longitudinal opening parallel to said cathode, a straight anode coated with fluorescent material positioned in registry with said opening for receiving electrons emitted by said cathode with suificient velocity to cause said anode to fluoresce and a control electrode between said cathode and straight anode for determining the portion of said straight anode to receive said electrons.

3. An electron discharge device having an envelope, a straight thermionic cathode within said envelope for emitting electrons, a cylindrical electrode surrounding said cathode and having a longitudinal opening parallel to said cathode, a straight rod anode coated with fluorescent material positioned in registry with the opening in said cylindrical anode and a variable pitch control grid comprising a helical coil surrounding said cathode, the pitch between the turns of said helical cell being progressively increased from one end of the grid to the other.

4. An electron discharge device having a thermionic cathode for emitting electrons, a cylindrical elecrode surrounding said cathode and having a longitudinal opening parallel to said cathode, a straight rod anode positioned opposite said longitudinal opening and coated with a fluorescent material and a variable pitch control grid positioned between said cathode and said rod anode for determining the length of the portion of said rod anode to receive electrons from said cathode.

5. An electron discharge device having an envelope, a straight thermionic cathode within said envelope for emitting electrons, a cylindrical electrode surrounding said cathode and having a longitudinal opening parallel to said cathode, a straight rod anode coated with fluorescent material positioned in registry with said opening for receiving electrons from said cathode with suflicient velocity to fiuoresce and electrically connected with said cylindrical anode and a control grid concentric with and surrounding said cathode and comprising a helical coil the pitch between the turns of which are progressively increased from one end of the grid to the other, said control grid decreasing progressively and lengthwise of the cathode the electron flow from said cathode to said rod anode when a progressively varying voltage is applied to the control grid whereby the length of the luminous portion of said anode is determined.

RICHARD TEMPEL ORTH. 

